1. Field of the Invention
The invention generally relates to a semiconductor device and method of manufacture and, more particularly, to a stress enhanced complementary metal-oxide-semiconductor (CMOS) device and method of manufacture.
2. Background Description
As semiconductor devices continue to evolve towards higher densities of circuit elements, the performance of materials used for the devices becomes more critical to overall performance, such as charge carrier mobility. One approach for enhancing performance involves imparting local mechanical stresses. In the case of a (100) Si surface orientation with current flow in the <110> direction, electron mobility and, thus, n-channel field effect transistor (nFET) performance, may be improved by imparting tensile stress along (i.e., parallel to) the direction of a current flow. Additionally, hole mobility and, thus, p-channel field effect transistor (pFET) performance, may be enhanced by imparting compressive stress parallel to the direction of current flow.
One approach for enhancing stress is to fabricate CMOS devices on substrates having a thin strained silicon (Si) layer on a relaxed SiGe buffer layer which exhibit substantially higher electron and hole mobility in strained Si layers than in bulk silicon layers. Furthermore, metal oxide semiconductor field effect transistors (MOSFETs) with strained Si channels exhibit enhanced device performance compared to devices fabricated in conventional (unstrained) silicon substrates. However, this traditional approach has several drawbacks. Specifically, no pFET improvement has been observed for Ge concentrations less than 30%. Furthermore, as Ge concentrations increase to a level required to enhance performance of p-channel field effect transistors, so does defect density. Dopant diffusion (e.g., of arsenic) is also problematic in SiGe layers and can lead to degraded short channel effects.
Another problem faced by conventional stress inducing techniques relates to achieving a balanced stress profile in the channel. Uneven stress profiles may result from non-uniform Ge distributions in SiGe layers, unevenly formed stress inducing films, and stress inducing structures that are unevenly spaced from a channel. Such irregularities are common occurrences that can diminish the beneficial effects of the stress inducing materials.
The invention is directed to overcoming one or more of the problems as set forth above.